In the copending application Ser. No. 253,258, a unique heating unit is described which can be formed as a unitary or monolithic all-ceramic body having a burner head at one end thereof, a combustion chamber downstream of the burner head, and a recuperator downstream of the combustion chamber in which two different fluids can be heated in successive zones.
As is pointed out in this application, a variety of heating systems having burners can be provided for the separate or combined heating of utility water and space-heating fluid (circulating water) utilizing either liquid or gaseous fuels and in which the fluid is heated by indirect heat exchange with hot combustion gases formed by the burner.
While such apparatus is provided in various sizes, configurations and heating capacities, it has been difficult heretofore to achieve high energy efficiency (high energy output with low fuel consumption) in a heating unit of small size, especially for the combined heating of utility water and the circulation of hot water of a space heating system.
The system described in the last-mentioned application greatly improves upon prior-art systems by forming the heating unit as a ceramic structure in which the burner head is a ceramic body having slit-like passages alternately fed with a combustion-sustaining medium such as air and with fuel, the air and fuel mixing at the burner mouth, or upon penetration of the fuel through porous walls between the passages, within the air passages.
This burner head is coupled with a ceramic recuperator body formed with slit-shaped channels, alternate ones of which pass the combustion gases while the others can be subdivided longitudinally into two zones for heating, in the upstream zone proximal to the burner chamber, the circulating hot water of the space heating system while the utility water is heated in the second zone.
This arrangement allows especially high energy efficiency to be obtained in a unit of small size, especially where both home-heating water and hot utility water are to be generated in the same unit.
Because the unit is composed of ceramic material, the combustion gases can be cooled during the indirect heat exchange process to temperatures below the dew points of these gases without creating any corrosion problems which might otherwise ensue because of the presence of acidic components in the combustion gases.
Other heating arrangements are known which occupy more space and thus have a lower volumetric efficiency or small energy output per unit of volume or weight and which also are less economical.
In these times of high energy cost, especially for liquid and gaseous fossil fuels, it is always of interest to improve the energy efficiency of a heating system.